Methods and apparatus for manufacturing shadow masks for colored television tubes

ABSTRACT

A MANUFACTURING METHOD AND APPARATUS FOR FORMING THE EDGES OF A SHADOW MASK INTO A SELF-SUPPORTING STRUCTURE IN WHICH ALL PORTIONS OF THE SHADOW MASK ARE FIRMLY SUPPORTED WHILE THEY ARE BEING SHAPED SO AS TO AVOID DESTRUCTION OR DISTORTION OF THE PERFORATED SECTION OF THE MASK. NINE INTERNAL SUPPORTING BLOCKS AND DIES ARE POSITIONED BY A ROTARY CAM AND AN AIR CYLINDER TO SUPPORT THE INSIDE CONCAVE SURFACE OF THE SHADOW MASK WHILE EIGHT DIES ARE BROUGHT IN FROM THE EXTERIOR OF THE MASK TO FORM THE EDGES INTO A SELF-SUPPORTING FLANGED AND RIBBED STRUCTURE.

NOV. 23, 1971 J. G, VALEK ETAL 3,621,699

METHODS AND APPARATUS FOR MANUFACTURlNG SHADOW MASKS FOR COLORED 'FELEVSON TUBES PRIOR ART [2 INVENTORS JOHN 6`. VLEK NOV. 23, 1971 1 G, VA K EVAL 3,621,699

METHODS AND APPARATUS R MANUFACTURING SHADOW MASKS FOR COLORED TELEVISION TUBES F'lled July l5, 1969 5 Sheets-Sheet owl Nov. 23, 1971 J G METHODS AND AP'PAR Filed July 15, 1969 MASKS FOR C VALEK ETAL 3,621,699 ATUS FOR MANUFACTURING SHADOW OLORED TELEVISION TUBES 5 Sheets-Sheet 5 NOV. 23, 1971 1 G VALEK ETAL METHODS AND APPARATUS FOR MANUFACTURING SHADOW MASKS FOR COLORED TELEVISION TUBES 5 Sheets-Sheet f1 Filed July l5, 1969 Nom 23, 1971 G, VALEK ETAL 3,621,699

METHODS AND APPARATUS FOR MANUFACTURING SHADOW MASKS FOR COLORED TELEVISION TUB ES Filed July l5, 1969 5 Sheets-Sheet 5 E\\\\\\\\\\ I.i ...ELE

SEQUENCE SEQUENCE HO VALVE VALVE 1 A TRANSDUCER TRANSDUCER TRANSDUCER 1 I 42\ 44\ 2 3 4 5 s 7 a /IOI [|00 UE HYDRAULIC 0 0 LV PUMP l u IIl.:I u u L1 lullltu u u 92 United States Patent O METHODS AND APPARATUS FOR MANUFAC- TURING SHADOW MASKS FOR COLORED TELEVISION TUBES John G. Valek, La Grange Park, and Myron C. Kirchner, Itasca, Ill., assignors to Tubal Industries, Inc., Elk Grove Village, Ill.

Filed July 15, 1969, Ser. No. 841,805 Int. Cl. B21d 11/:04, 22/ 00, 51/00 U.S. Cl. 72-306 11 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND O'F THE INVENTION Conventional colored television shadow masks contain a curved forarninous or translucent area formed by a multitude of miniature apertures through the center portion of a metal sheet surrounded by an imperforate border section. In the prior art, the outside edge of the imperforate border section has been drawn down into four sides which are generally perpendicular to the foraminous portion. The mask is then mounted in a convenient fashion to a mounting ring. The mounting ring serves to stabilize the mask and support it within the picture tube. This technique is cumbersome, lengthy, expensive, and results in a heavy shadow mask assembly. In addition, large temperature gradients in the assembly often cause the shadow masks to warp, resulting in a misalignment of the shadow mask and a loss of fidelity in the color picture. A recent improvement in shadow -masks eliminates this mounting ring by shaping the four imperforate sides into a self-supporting structure. This new type of shadow mask is much less costly, lighter in weight, does not warp, and is referred to in the industry as a uniframe mask or unimask. Although the unframe mask is a tremendous improvement in the art, there has been till now no simple method of manufacturing uniframe masks.

SUMMARY OF THE INVENTION Briefly, the present invention operates to form the uniframe mask from the same drawn down shadow mask that is welded to the support ring in the prior art. This drawn down shadow mask is positioned over nine internally supporting dies. A rotary cam operates to slide eight of these supporting dies radially outward to the inside dimension of the desired unifrarne shadow mask. The ninth supporting die is raised into the remaining center position, mechanically holding the other eight supporting dies in position. In this configuration, the nine support dies form a composite supporting surface shaped exactly like the inside of the desired shadow mask. At this point in time, four clamps are lowered manually or by means of air cylinders onto the top four corners of the shadow mask to hold it firmly in place and prevent distortion of the central perforated translucent area. Subsequently, eight additional dies are brought in around the circumference of the shadow mask by means of eight 3,621,699 Patented Nov. 23, 1971 ICC hydraulic cylinders. The external dies compress the sides of the shadow mask assembly into ribbed self-supporting structures and simultaneously tuck under the sides so as to form a right angle bend in the sides of the shadow mask assembly. Fonmed into this shape, the shadow mask is self-supporting and need not be welded to a support ring as in the prior art. To permit removal of the finished uniframe mask, the eight external dies are withdrawn, the four clamps raised, and the nine internal support dies 'withdrawn into their retracted positions. Thus, it is an object of my invention to provide a method for manufacturing uniframe shadow masks. \A further object of my invention is to provide a method and apparatus to form a self-supporting shadow mask in a single operation. Other objects and `advantages will become apparent to those skilled in the art upon consideration of the following description and drawings.

BRIEF DESCRIPTION OF THE DRAIWINGS FIG. 1 shows the beginning drawn down shadow mask used in any invention.

FIG. 2 shows the finished uniframe mask as produced by the machine and method of my invention.

FIG. 3 is a perspective view of some of the major elements of the present invention mounted on an operating table.

FIG. 4 is a sectional view of the apparatus of FIG. 5 taken along the line indicated 4 4 in FIG. 5.

FIG. 5 is a schematic view of the top of the machine shown in FIG. 3 with the internal supporting dies expanded into the composite shape position.

IFIG. 6 is another schematic View of the top of the machine with the internal dies retracted.

lFIG. 7 is a partial sectional view taken along the line 7--7 in FIG. 5, showing for the first time the corner clamps lwhich hold the shadow mask down.

FIGS. 8a and 8b show two examples of the dies used in the invention.

FIG. 9 is a schematic representation of the electrical, air, and hydraulic circuitry which operates the machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 a shadow mask is shown which is generally referred to in the industry as a deep drawn shadow mask. The mask is constructed from a thin sheet of stainless steel and has a translucent or foraminous area 10 which is made up of a multitude of small holes which allow the passage of electrons to the face of the picture tube. The foraminous area 10 is surrounded by an imperforate or opaque border region 12 which is drawn down into four side walls 14. At one time, deep drawn shadow masks such as this were mounted by welding them to heavy support rings. lHowever, as already mentioned, it has been discovered that the side walls 14 may be tucked under and elnbossed to form a self-supporting structure such as shown in FIG. 2. In FIG. 2 the walls 14 are tucked under to form a flange 16 and a number of reinforcing ribs or grooves 18 have been embossed thereon. The present invention provides a method and apparatus for forming the unifrarne mask or unimask of FIG. 2 from the deep drawn mask of FIG. 1.

FIG. 3 shows some of the maj-or components of the invention. A frame table 20 is used to support a slanted working base 22. Mounted on Ibase 22 is a slotted guide bed member 24 upon which the external corner dies 26 and the external side dies 28 rest. Riding in the slots in slotted guide bed 24 are eight slide bars 30 upon which are securely mounted four internal corner dies 32 and four internal side dies 34. Inside internal dies -32 and 34 is a plug 36 which locks all of the cam driven internal dies into .three sets are shown in FIG. 3. Each external die is guided by means of a pair of leader pins 38 and actuated by hydraulic cylinders 40 on the sides and hydraulic cylinders 41 on the corners. To activate the machine, the operator must press a pair of switches 42 and 44. Two switches are used as a safety factor, requiring the use of both of the operators hands so that there is no possibility of the operator getting one of his hands into the machinery. Upon activating both switches, an air cylinder, not shown in FIG. 3 and mounted underneath the table, retracts plug 36 into a receiving hole in bed 22. At this point in time, a second air cylinder under the table rotates a cam under the table which retracts internal dies 32 and 34 along with v their respective slide bars 30 inward into the space left vacant by plug 36. This permits the operator to lower the deep 4drawn shadow mask of FIG. 1 over the internal dies 32 and 34. The operator then reactivates switches 42 and 44 to continue the cycling of the machine. The abovedescribed sequence of steps is reversed and the internal dies 32 and 34 expand to their maximum radial position. Plug 36 is again raised into the position shown in FIG. 3 to lock dies 32 and 34 into their proper positions. lInternal dies 32 and 34 press rmly against the inside walls of the deep drawn shadow mask. The translucent center portion is now clamped firmly down to the top of dies 32 and 34 and plug 36 by means of four clamps which will be described with reference to FIG. 7. At this point in time hydraulic cylinders 40 are actuated, bringing external side dies 28 in to press ribs 18 into the side walls 14 of the deep drawn mask. Simultaneously, the stepped lower edge on external side dies 28 folds under side Walls 14 to form ange 1'6 as shown in FIG. 2. vIt should be noted that a sequence valve in the hydraulic system operates to actuate side external dies 28 to emboss and tuck under the sides before corner external dies 26 are activated so as to prevent ripping the metal. Finally, hydraulic cylinders 41 move corner dies 26 in to emboss corner ribs and tuck under the corners. A more detailed examination of the components of FIG. 3 may be had by reference to FIGS. 4, 5 and 6.

PIG. 5 is a schematic top view of the components of FIG. 3 with the dies in the same positions as in FIG. 3. In FIG. I6 a similar schematic view is utilized but the internal ldies are retracted into their innermost positions. FIG. 4 is a sectional view of the apparatus -of FIG. 5 taken along section line 4-4. In FIG. 4 center plug 36, internal side dies 34, and slide bars 30 are again shown along with external side dies 28 and hydraulic cylinders 40, all mounted on flat base 22. The air cylinder used to lower plug 36 is shown as cylinder 46 mounted to a circular mounting block 48. Cylinder 46 operates to lower plug 36 by driving a bracket 50 downward which moves four leader pins 52 connected to plug 36. `Only two of the leader pins 52 are shown in FIG. 4. Mounted on plug 36 are two guide blocks 51 which drop into holes 49 when plug 36 is lowered. Beveled edges on blocks 51 meet beveled edges on slide bars 30 to safeguard against plug 36 ever striking dies 34. Although only two blocks 51 are shown, there are eight in all, one for each slide bar 30. Of course, there are also eight holes 49.

Surrounding circular mounting block 48 is an annular rotary cam 54. Cam 54 is operable to rotate about circular block 48 upon a set of rollers 56. Rollers 56 are mounted in mounting blocks 58, which are'securely fastened to mounting block 48. Although only two rollers 56 are shown, more are desirable and the preferredembodiment uses eight. It should be noted that none of the mounting bolts or fasteners are shown in these draw-` ings in order to provide a clearer picture of the 4 operational characteristics of the invention. Cam S4 also rides on a thin wear plate 60 which helps to further locate cam 54. Cam S4 is rotated by an air cylinder 62 which is mounted in any suitable fashion to base 22 and connected to cam 54 by means of an arm 61 and a pin 64. Six spiral grooves are machined into the top yof cam 54. Each slide 30 has a follower pin 70 connected thereto which passes through a slot 72 iu base 22 and rides in one of the spiral grooves in cam 54. The operation of air cylinder 62 and the spiral grooves in cam 54 may be better understood yby reference to FIG. 6.

As can be seen in FIG. 6, cam 54 is rotated by air cylinder `62 which is connected by a pivoting arm 61 to pin 64 in cam 54. Expansion of the piston of cylinder 62 rotates cam 54 suciently so that the pins 70 riding in the grooves of cam 54 move slides 30 radially in or out, depending on the direction of rotation of cam 54. Since the internal dies 34 and 32 are connected directly to slides 30, they also move in or out, respectively. There are only six grooves in cam 54, the two long grooves being identical and operating with two pins 70 apiece. The remaining shorter grooves are identical in design on opposite sides of cam 54 and each of them operates to drive one of the remaining four pins 70.

In FIG. 6, plug 26 is shown beneath the internal dies in a retracted position in at 4base 22. Base 22 is not shown in FIG. 6. Expansion of the internal dies is accomplished by activating air cylinder 62 and rotating cam 54 clockwise. -Each of the follower pins 70 travels outward in its spiral groove, pulling on sides r30 which are connected to the internal dies 32 and 34. Corner dies 32 move rst and as they reach their final positions, side internal dies 34 move to ll in the gaps. Then air cylinder 46, shown in FIG. 4, raises center plug 36 into the locking position so that the internal dies take the conguration shown in FIG. 5.

In FIG. 5, cam 54 and part 0f one of its grooves is visible through a cutaway in base 22. In addition, one of the slots 72 in base 22 is clearly visible. Slots 72 allow follower pins 70 to travel in and out in base 22 as they follow the spiral grooves in cam 54. Internal dies 32 and 34 would now be expanded inside a shadow mask such as shown in FIG. l. The actual shadow mask is not shown in FIG. 5 in order to provide a clearer View of the apparatus. At this point in time, the side of the mask may be embossed with ribs and tucked under to form the flange 16 shown in FIG. 2. However, before the external dies are activated, four clamps are brought down on the tops of corner internal dies 32 to hold the shadow mask firmly to the surface and prevent damage to the central foraminous area of the mask. These clamps are not shown in FIG. 5 but, rather, in FIG. 7.

In FIG. 7 one of the hold down clamps 76 is shown which may be pushed into position manually or by means of a rotating air cylinder 78 and a connecting ar-m 80. Four such assemblies are utilized in the preferred embodiment, each one mounted on a plate 82 which is in turn mounted to the top of base 22 by any suitable means. In FIG. 7 plate 82 is mounted directly to the top of a leader pin assembly 38. Four cylinders 78 and four clamps 76 are used, one set at each corner of the shadow mask, although only one set is shown in FIG. 7 for the purpose of clarity.

Referring again to FIG. 5, typical external corner dies 26 and side dies 28 may -be seen resting on guide bed 24. Actually, they rest on suitable wear plates which are not shown in the figures. After plug 36 has secured the internal dies in their expanded position and all four of the overhead clamps 76 have secured the shadow mask to the top surface of the plug 36 and the internal dies 32 and 34, external side dies 28 are forced inV by hydraulic corner external dies 26 come in. This particular sequence prevents any distortion or tearing of the metal bunched in at the corners. In FIG. the small rib forming dies 90 are shown, recessed into grooves in the external dies 26 and 28. Each of these small rib forming dies 90 is aligned with a small similar female groove in the internal dies 34 and 32 so as to emboss the rib structure into the side walls of the shadow mask. This is more readily seen in FIGS. 8a and 8b.

In FIG. 8a the end view of the assembled internal dies is shown and may be compared to one of the end forming external side dies shown in FIG. 8b. Internal dies 32 and 34 come together to form a smooth surface having grooves therein suitable to form the supporting structural ribs. In FIG. 8b the small rib forming dies 90 are shown inserted in grooves in die Z8. Small pieces of metal are used to form dies 90 so that the entire die 28 need not be replaced in the event of a small fracture in one of the individual rib forming dies. It is also apparent from FIGS. 8a and 8b how the small step portion 92 of die 28 is positioned so as to tuck under the internal dies 32 and 34 and form the tucked under flange 16.

In FIG. 9 a schematic of one of many possible air, hydraulic, and electrical circuits is shown in diagrammatic form. A hydraulic pump 100 provides pressurized hydraulic fluid while an air pump 106 provides pressurized air. When the operator engages switches 42 and 44, a signal is presented to a sequence valve 101. Sequence valve 101 operates to deliver pressure to the various outputs in a timed sequential order. The first output is on line number 1 which activates a transducer 103 which in turn activates cam rotating air cylinder `62 so as to bring the internal dies into position inside the shadow mask. Sequence valve 101 then directs iluid to line 2 and a transducer 102 which activates an air sequence valve 104. Air sequence valve 104 first activates air cylinder 46, which serves to raise center plug 36 into position. This operation complete, sequence valve 104 sends a signal to the four air cylinders 78 which lower clamps 76 into position on top of the shadow mask. Sequence valve 101 now delivers fluid to line 3 and hydraulic cylinders 40 which activate the external side dies to press the sides into position. Sequence valve 101 then directs fluid to line 4 which operates the hydraulic cylinders for the external corner dies. The uniframe mask has now been completely stamped and processed and the machinery must withdraw in order to allow the operator to remove the finished product. To accomplish this, sequence valve 101 continues cycling, delivering a fluid signal to lines `5 and 6 sequentially. This retracts cylinders 41 and 40, bringing the external dies back into their rest position. Sequence valve 101 then delivers iiuid to line 7 and a transducer 108 which activates another air sequence valve 110. Sequence valve 110 operates first to withdraw clamps 76 by retracting air cylinders 78 and then operates to withdraw plug 36 by deactivating air cylinder 46. Sequence valve 101 then delivers a signal to line 8 which signals transducer 103 to deliver air to cylinder 62 so as to cause it to rotate cam 54 counterclockwise and retract the internal dies toward the center, allowing the removal of the finished uniframe mask. Clearly, the particular detailed design configurations shown in the drawings may be varied over a wide range and still perform the function of shaping a uniframe shadow mask. Since not all possible variations can be mentioned or shown in the drawings, we do not intend to be bound thereto except `as defined by the appended claims.

We claim:

1. A method of forming uniframe shadow masks from drawn down shadow masks having a central forarninous portion surrounded by wall portions comprising the steps of positioning all portions of the drawn down mask in predetermined positions, holding and isolating the central foraminous portion to protect it from any mechanical stresses, and simultaneously compressing all of the wall portions of said mask into flanged and ribbed supporting members.

2. A method of forming drawn down shadow masks into uniframe shadow masks comprising the steps of supporting the drawn down mask over substantially all of its concave surface with a rst set of characterized blocks; moving said first set of blocks to position-substantially all of the concave surface and sides of the drawn down mask to the dimensions of the desired uniframe mask; pressing the mask against the first set of blocks to prevent any change in shape of the center portion of the mask; impressing ribs into the side areas of the mask; bending the sides of the mask under the first set of blocks toward the center; impressing the ribs into the corner areas of the mask; bending the corners of the mask under the rst set of blocks toward the center; releasing the mask from the first set of blocks; and withdrawing the first set of blocks from the concave surface to permit removal of the uniframe shadow mask.

3. The method of claim 2 in which the first characterized set of blocks are moved radially by a rotary camming action, the side rarea ribs are impressed and the sides are bent under simultaneously by moving a second set of stepped characteristic blocks radially to compress the mask against said first set of blocks, and the corner area ribs are impressed and the corners bent under simultaneously by moving a third set of steped blocks radially to compress the mask against said first set of blocks.

4. A machine for forming a drawn down shadow mask into a uniframe shadow mask comprising:

a base;

a plurality of internal blocks having a composite shape substantially equal to the inside concave shape of the unframe mask and being movably mounted on said base;

means for moving said internal 'blocks into the composite shape position against the inside of the drawn down mask and for withdrawing said blocks from within the uniframe mask;

means for holding said mask to said internal blocks when the blocks are in the composite shape position;

a plurality of external blocks having an assembled shape substantially equal to the outside perimeter shape of the uniframe mask; and

means for moving the external blocks into the assembled shape position and against the perimeter of said drawn down mask in conjunction with said internal blocks to form the uniframe mask.

S. The apparatus of claim 4 in which said internal and external blocks comprise dies mounted so as to slide generally radially on said base, the internal dies moving outward within the drawn down mask and the external dies moving inward in order to shape the sides of the mask against the internal dies.

6. The apparatus of claim 5 in which said internal blocks also include a center plug die operable to move generally perpendicular to said base into the space between said internal dies and thereby lock said internal dies into their composite position.

7. The apparatus of claim -6 in which said means for moving the internal dies comprise a rotating cam adapted to engage said plurality of internal dies and move the internal dies radially upon rotation thereof.

8. The apparatus of claim 6 in which said means for moving the external blocks comprise hydraulic means ladapted to engage said external blocks and move them into and out of said assembled shape position.

9. The apparatus of claim 7 in which said means for moving the external blocks comprise hydraulic means adapted to engage said external blocks and move them into and out of said assembled shape position.

10. The apparatus of claim 9 in which said cam, said means for holding the mask and said center plug die are actuated by air cylinders.

11. The apparatus of claim 10` including control means operable to regulate the hydraulic means and air cylinders so as to cause sequential operation of the internal dies, the center plug, the holding means, and the external dies.

References Cited UNITED STATES PATENTS Fiore 29-163.5

Moller 72--348 Hamilton et a1. 178--7.f82 Holtzhauer 72-404 8 3,435,268 3/ 1969 Rublack 29`25.18 59,104 10/1866 Way 72--309 RICHARD I. HERBST, Primary Examiner 5 M. J. KEENAN, Assistant Examiner U.S. C1. X.R. 

